Rainwater harvesting in the water and sanitation plumbing code for Jordan
In 2011, a research project was conducted in Jordan to generate information to assist in designing effective rooftop water harvesting schemes. The researchers studied rainwater patterns, annual precipitation, the cost of water tanks and other necessary technology, and water values. The optimal size of the technology depends on the local value of these variables. The advantages and disadvantages of rooftop water harvesting are also considered to aid well-informed decision making.
Based on the results of this research, the Ministry of Public Works and Housing (MPWH), in cooperation with MWI, has recently included rainwater harvesting in the new water and sanitation plumbing code. This code illustrates where and how rainwater harvesting is feasible and cost-effective. The reader is referred to this code for details related to feasibility of rainwater harvesting and the design of rainwater collection systems.
The capture and utilisation of rainwater (or rainwater harvesting – RWH) is an ancient tradition that resembles techniques used in today’s Jordan around 5,000 years ago. Agriculture using surface runoff and rain harvesting techniques were extensively practiced in earlier times. Some of these structures are in good operating condition, such as the Roman pools near Ajlun, Madaba and Mwagger. Rainwater can provide water for both domestic and irrigation uses. Jordanians continue to collect rainwater in spite of the availability of water distribution systems due to the shortage of water. In fact, there is rapidly growing interest in rainwater harvesting and storage as a potential water supply to meet part of urban and rural water demand.
In this 2011 study, the rainwater harvesting potential for municipal use in rural and urban areas in Jordan has been reviewed. In addition, the feasibility of rainwater harvesting across Jordan has been investigated. The study provides specific recommendations on the most appropriate methods and technologies adapted to Jordan. Tangible figures on quantities of collected water, water quality, impacts on health and the environment, appropriate designs of water harvesting systems, and cost-benefit analyses are also provided.
The amount of collected water
In the study, water harvesting yields are calculated for 27 roof areas ranging from 100 m2 to 1,000 m2. These roof areas cover residential buildings (single houses, villas and apartments) and public, commercial and industrial roofs. The rainfall data used in the study represents 17 rainfall zones ranging from 50 mm to 850 mm of annual rainfall. The results reveal that potential harvested water that could be obtained from a roof with an area of 100 m2 may range from 4 m3 to 68 m3 for rainfall zones ranging from 50 mm to 850 mm.
The potential annual harvested rainwater in m3 from different roof areas and rainfall can be estimated with the following formula:
- Potential water harvest (m3/year) = Roof area (m2) * annual rainfall (mm) *0.0008
According to the Population and Housing Census of 2004 Conducted by the Department of Statistics, about 33,229 rainwater cisterns existed at that time in Jordanian governorates and used as a main source of drinking water. For instance, a home in Amman that receives 350 mm average annual rainfall and has 200 m2 of roof area, the potential rainwater that can be captured is approximately 56 m3. This is sufficient to supply a family of five people for approximately 140 days, based on the current average water supply of 80 litres per capita per day. Potential rainwater harvesting in various Jordanian governorates for varying sizes of collection areas is illustrated in the new water and sanitation plumbing code. The amount of rainwater storage that would be cost-effective to build is based on the monthly inflows of harvested rainwater, the monthly extracted water-use, and the storage construction cost.
Costs, benefits and optimal tank size
The water storage tank usually represents the biggest capital investment element of RWH systems, and therefore requires careful design to provide optimal storage capacity while keeping the costs as low as possible. Installing a water harvesting system at household level can cost anywhere from JAD 400 to more than JAD 2,000. It is difficult to make an exact estimate of cost because it varies widely depending on the availability of existing structures, like pipes, tanks and other materials. Actual cost depends on the final design and size of the tank. The cost is comparatively less if the system is incorporated during construction of the building.
Regarding the cost of the tanks, the most important equipment within a RWH system, the average cost for a pear-shaped tank with a maximum size of 50 m3 is about JAD 33 per m3, while for a concrete tank the cost may range from JAD 60–100 m3. It should be noted that the cost varies from one location to another. The above costs are used only to perform the economic feasibility of the proposed tank sizes for different rainfall zones and roof areas. Estimating the total cost of concrete tank involves the consideration of all the materials involved in the production of the system (steel, concrete, pipes, pumps, steel gate, plastering and isolation), excavation and the required labour for construction. The system proposed, if feasible, would be in use for many years (close to the lifespan of the building); hence future costs and benefits will have to be discounted before computing total cost. The construction and installation costs of rooftop rainwater harvesting could cost as little as JAD 2,000 for a tank size less than 20 m3, and might go up to JAD 6,000 for a tank size of around 100 m3. Figure 1(See image) shows how the overall system cost typically rises with increasing tank volume, even as system costs per cubic metre of storage dropSee image)
Cost-benefit analyses of two roof harvesting systems (pear and concrete tanks) were applied in the report. When calculating the costs and benefits of roof water harvesting, the unit price of water (from regular sources, whether piped water or truck delivered water) is an important factor in deciding whether the proposed system is economically feasible or not. The results revealed that pear-shaped tanks will be economically feasible in all rainfall zones when 1 dinar per cubic metre is assigned as the value of harvested water. Concrete tanks will not be economically feasible at this level, as they require a higher water value.
The optimal tank size for any roof area depends on the amount and seasonal distribution of rainfall, the unit cost of the tank, and the value of water (price of water from the utility or truck based water vendors).
Implementability of roof water harvesting
Having a positive benefit-cost ratio alone does not automatically increase the utilisation of rainwater harvesting. Several other conditions are involved, such as:
- A team of trained plumbers who can estimate costs and the optimal size of the storage system, and are able to implement projects on site;
- It is important to monitor and learn from implemented projects;
- Public awareness is a prerequisite for widespread use of RWH;
- Government commitment in enforcing the Roof Water Harvesting Code is very important towards achieving successful implementation of this measure;
- Cultural perceptions and religious views regarding the use of water, as well as traditional preferences for its location, taste, smell or colour, are all important and to be taken into consideration; and
- It is important to know the people, to be aware of their concerns, and to encourage their participation at every step of the rainwater harvesting process. It has been shown that the more a community is involved, the greater the potential for a successful project. These and likely other factors not mentioned here can positively or negatively affect an RWH system.
Adoption of this technology requires a “bottom up” approach rather than the more usual “top down” approach employed in other water resource development projects. This may make rainwater harvesting less attractive to some governmental agencies tasked with providing water supplies in developing countries, but the mobilisation of local government and NGO resources can serve the same basic role in the development of rainwater-based schemes as water resources development agencies within larger, more traditional public water supply schemes.
Advantages and disadvantages
There are also some clear advantages of RWH, such as:
- The size of the system can be adapted to the roof size and the climate;
- It is one of the easiest and cheapest methods of providing a good water supply to urban and rural communities in Jordan;
- RWH does not require mobilising vast quantities of resources and importing materials and expertise, as compared to those involved in the planning and building large dams and reservoirs;
- A small RWH and storage system relies and builds on local skill and experience in construction, water consumption rate and rainfall patterns;
- RWH maintenance is easy; and
- RWH can be an essential resource during recurring periods of drought.
Rainwater harvesting technologies present the following disadvantages as well:
- RWH is susceptible to limited supply and uncertainty of rainfall;
- There is a high initial cost of building the permanent storage facilities (the primary expense is the storage tank);
- The quantity of rain water available depends on rainfall, and for long periods of drought it is necessary to store an excessively large volume of water;
- Collected rainwater may not be fit for human consumption without additional screening and/or adding necessary minerals; and
- As rainfall is usually unevenly distributed throughout the year, rainwater collection methods can serve as only supplementary sources of household water.
- A study is available to help promote the widespread use of rooftop water harvesting, but there is no data resulting from the study on the actual utilisation of the technology.
- Proper choice and sizing of technology is important for successful rooftop water harvesting. Constructing a rooftop water harvesting system together with the construction of a building reduces costs. The information is available but it needs to reach citizens and building operators — so communication is critical.
- Potential annual harvested rainwater in m3 from different roof areas and rainfall amounts can be calculated with the following formula: potential harvest (m3/year) = Roof area (m2) * annual rainfall (mm) *0.0008
- Unit cost of tanks for rooftop water harvesting
This practice is repeatable in arid regions. If there is too little rain with high seasonality, the scheme’s financial viability becomes uncertain.
- Installing a water harvesting system at household level can cost anywhere from JAD 400 to more than JAD 2,000. If the value of water from alternative sources (tap water, truck delivered water) is above 1 dinar per m3, then rooftop water harvesting can become economically viable.
Fayez Abdulla: email@example.com
- Abdulla F. A. and Al-Shareef A. W. “Roof rainwater harvesting systems for household water supply in Jordan”, Desalination, 243 (2009), pp. 195–207.
- Abdulla F. A. “Rainwater Harvesting in the Water and Sanitation Plumbing Code”, report submitted to the USAID-funded IDARA project, Amman, Jordan, 2011.
- Abdalla, Fayez. “Rainwater Harvesting Potential for Municipal and Industrial Use in Rural and Urban Areas in Jordan”, 2001.
- Jordanian National Building Council, “Jordanian New Water Supply and Sanitation Plumbing Code”, 2011.